URI student uncovers threat to butterfly population
Invasive plant kills monarch larvae

KINGSTON, R.I. -- September 12, 2000 -- North Kingstown resident Jennifer Dacey, a senior at the University of Rhode Island, spent the summer investigating an invasive plant that could reduce local populations of monarch butterflies.

Working with URI Professor Richard Casagrande, Dacey studied black swallowwort, a plant native to Europe that kills the larvae of America's most popular butterfly.

"The objective of my study was to see how this invasive plant affects monarch populations," said Dacey. "Our laboratory made what we believe is the first scientific observation of monarch's laying eggs on black swallowwort."

That behavior could be bad news for the butterfly.

Monarch caterpillars feed exclusively on milkweed, a common native plant that serves as a host to several insect species. Each adult female monarch lays 200 to 300 eggs in the summer.

"If they lay their eggs on black swallowwort, the eggs hatch but the larvae don't survive," Dacey explained. "That's most likely because the plant has a different toxicology than milkweed, so after feeding on it once, they die."

Black swallowwort was brought to New England in the 1800s to cultivate as an ornamental plant, but it quickly spread throughout the Northeast. It grows in disturbed areas like roadsides, and has begun to expand into backyards and natural areas. The plant is difficult to control with herbicides, and even pulling it out by hand doesn't eliminate it.

"There aren't any native insects that keep it under control here, and it usually outcompetes native vegetation," Dacey said.

Dacey studied captive monarchs in cages in a lab and in the field, and she checked more than 1,000 black swallowwort plants in fields in North Kingstown, Wakefield, Kingston and Jamestown during July and August. She observed that monarchs prefer to lay eggs on milkweed, but a substantial portion of their eggs are laid on swallowwort. If this invasive weed continues to spread, it might seriously reduce monarch populations.

Dacey's research was funded by the URI Coastal Fellowship Program, a unique program designed to involve undergraduate students in addressing current environmental problems. Sponsored by the URI Cooperative Extension and now in its fifth year, the Coastal Fellowship Program teams students with URI faculty, research staff and graduate students to help undergraduates gain skills that will ensure their future success.

Following graduation in May 2001, Dacey hopes to conduct additional fieldwork involving mammals, birds or insects.

"My black swallowwort research has given me a greater appreciation for plants," she said. "I believe my Coastal Fellowship played an important role in setting a foundation for my future endeavors and gave me a competitive edge in the process."

For Information: Todd McLeish 874-7892